| 华南桂东南地区加里东期Ⅰ型花岗岩类的岩石成因及构造意义 |
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| 引用本文： | 刘明辉,时毓,唐远兰,赵增霞,刘希军,高爱洋,黄椿文.华南桂东南地区加里东期Ⅰ型花岗岩类的岩石成因及构造意义[J].地球科学,2021,46(11):3965-3992. |
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| 作者姓名： | 刘明辉 时毓 唐远兰 赵增霞 刘希军 高爱洋 黄椿文 |
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| 作者单位： | 1.桂林理工大学广西隐伏金属矿产勘查重点实验室, 广西桂林 541004 |
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| 基金项目： | 国家自然科学基金项目41862003国家自然科学基金项目41562005广西杰出自然科学基金项目2019GXNSFFA245005广西杰出自然科学基金项目2018GXNSFFA281009内生金属矿床成矿机制研究国家重点实验室(南京大学)开放基金项目2020-LAMD-K09 |
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| 摘 要： | 龙新岩体和夏郢岩体位于扬子地块与华夏地块拼合带的西南端，岩体中的Ⅰ型花岗岩成因研究对揭示桂东南地区早古生代的地球动力学背景及其构造演化具有重要的地质意义.对龙新岩体的寄主岩和其暗色微粒包体，以及夏郢岩体岩石进行了LA-ICP-MS锆石U-Pb定年、Lu-Hf同位素和全岩地球化学研究.锆石U-Pb定年结果显示，龙新岩体的寄主岩（花岗闪长岩）的年龄为440±2 Ma；龙新岩体的暗色包体（闪长岩）的年龄为441±1 Ma，寄主岩与暗色包体为同期岩浆作用的产物.夏郢岩体花岗闪长岩和二长花岗岩年龄分别为447±3 Ma和436±3 Ma，说明夏郢岩体至少发生了2期岩浆侵入事件.Hf同位素研究表明，龙新岩体寄主岩和暗色微粒包体的锆石εHf（t）值分别为-3.32~-5.83和-17.89~-1.82，二阶段模式年龄（TDM2）分别为1.62~1.76 Ga和1.57~2.54 Ga；夏郢岩体早期花岗岩闪长岩和晚期二长花岗岩的锆石εHf（t）值分别为-15.43~3.03和-4.79~6.82，TDM2分别为1.59~1.99 Ga和0.97~1.70 Ga，指示物源主要来自古-中元古代的地壳物质.地球化学特征表明龙新岩体寄主岩为准铝质高钾钙碱性Ⅰ型花岗岩，寄主岩和暗色微粒包体均富集轻稀土元素和大离子亲石元素，亏损重稀土元素及高场强元素；夏郢岩体早期的花岗闪长岩为弱过铝质高钾钙碱性Ⅰ型花岗岩，晚期的二长花岗岩则为强过铝质高钾钙碱性Ⅰ型花岗岩，主微量元素特征均与龙新岩体寄主岩相似.根据研究区花岗岩和镁铁质包体的岩相学、年代学、地球化学及Hf同位素组成特征，表明龙新岩体的暗色包体（闪长岩）为岩浆混合成因，而龙新岩体寄主岩（花岗闪长岩）和夏郢岩体（早期花岗岩闪长岩和晚期二长花岗岩）具有一致的岩石源区和岩石成因，但在后期的成岩过程中存在岩浆混合和结晶分异程度的差异.综合以往对华南地区构造背景的研究，认为龙新和夏郢岩体是在扬子地块和华夏地块陆内造山期后，岩石圈伸展减薄，热的幔源岩浆上涌底侵，中-下地壳受到地幔热影响发生部分熔融，形成的酸性岩浆在源区和基性岩浆经历了不均一且不强烈的壳-幔混合作用形成的.
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| 关 键 词： | 加里东期 Ⅰ型花岗岩 锆石年代学 龙新岩体和夏郢岩体 桂东南 地球化学 岩石学 |
| 收稿时间： | 2021-02-09 |
Petrogenesis and Tectonic Significance of Caledonian I-Type Granitoids in Southeast Guangxi,South China |
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| Liu Minghui,Shi Yu,Tang Yuanlan,Zhao Zengxia,Liu Xijun,Gao Aiyang,Huang Chunwen.Petrogenesis and Tectonic Significance of Caledonian I-Type Granitoids in Southeast Guangxi,South China[J].Earth Science-Journal of China University of Geosciences,2021,46(11):3965-3992. |
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| Authors: | Liu Minghui Shi Yu Tang Yuanlan Zhao Zengxia Liu Xijun Gao Aiyang Huang Chunwen |
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| Abstract: | The Longxin and Xiaying plutons are located in the southwest of the Yangtze and Cathaysia blocks collision belt, studying the petrogenesis of the Ⅰ-type granitoids is of great geological significance to reveal the geodynamic background and tectonic evolution of the Early Paleozoic in Southeast Guangxi. LA-ICP-MS zircon U-Pb dating, geochemical and Lu-Hf isotopic data are reported for the host rock and its mafic microgranular enclave (MME) of Longxin and Xiaying plutons. Zircon U-Pb dating results of samples from the Longxin and Xiaying plutons show that the age of the host rock (granodiorite) of the Longxin pluton is 440±2 Ma, and that of the MME (diorite) of the Longxin pluton is 441±1 Ma, showing that the host rock and the MMEs are the products of the simultaneous magmatism. The age of the granodiorite and monzogranite of Xiaying pluton are 447±3 Ma and 436±3 Ma, indicating that there were at least two stages of intrusion in the Xiaying pluton. Both the host rocks (granodiorite) and MME (diorite) of the Longxin pluton have negative εHf(t) values (-3.32 to -5.83 and -17.89 to -1.82), and the corresponding two-stage model ages (TDM2) are 1.62-1.76 Ga and 1.57-2.54 Ga, respectively. The zircon εHf(t) values of the granodiorite (early stage) and monzogranite (late stage) of the Xiaying pluton are -15.43 to 3.03 and -4.79 to 6.82, respectively, with the TDM2 model ages of 1.59-1.99 Ga and 0.97-1.70 Ga, respectively, indicating that the parental magma of the granitic rocks might have originated mainly from crustal materials of the Paleoproterozoic-Mesoproterozoic. Geochemical data exhibit that the host rocks of the Longxin pluton are peraluminous high-K calc-alkaline Ⅰ-type granite, with relatively high light rare earth elements (LREE) and large ion lithophile elements (LILE), with low high field strength elements (HFSE) and heavy rare earth elements (HREE). For the Xiaying pluton, the granodiorite (early stage) is weakly peraluminous high-K calc-alkaline Ⅰ-type granite, while the monzogranite (late stage) is peraluminous high-K calc-alkaline Ⅰ-type granite, which is similar to the host rocks of the Longxin pluton. According to the petrography, geochronology, geochemistry and Hf isotopic composition characteristics of granites and mafic inclusions in the study area, indicating the MME (diorite) of Longxin formed by the magma mingling and mixing, although the host rock (granodiorite) of the Longxin and Xiaying plutons (granodiorite and monzogranite) have similar sources and petrogenesis, which have differences in magma mixing and fractional crystallization in the formation of granites. Based on previous studies on the tectonic setting in South China, it is suggested that the Longxin and Xiaying plutons were formed by the extension and thinning of the lithosphere, upwelling and underplating of the hot mantle-derived magma after the intra-continental orogeny of the Yangtze and Cathaysia blocks. The lower crust was partially melted under the influence of mantle heat and formed the acid magma, and then mixed with the mafic magma for limited and uneven degrees of crust-mantle mixing in the source region. |
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